1. Field of the Invention
This invention relates to a process for the treatment of rubber and plastic wastes and, in particular, to a method for converting such material to liquid and gaseous fuels and chemicals by catalytically cracking a mixture of the solid polymeric wastes and selected petroleum-derived streams.
2. Description of the Prior Art
Given the proliferation of used rubber tires, plastic packaging materials, one-way plastic containers, and by-product and substandard polymers, improved methods of recovering the hydrocarbon values contained therein are needed, particularly in view of the increasing scarcity of oil and natural gas. The potentially valuable hydrocarbons in such materials would be better utilized if an economically attractive method could be devised for transforming them into useful liquid, solid, and/or gaseous hydrocarbon products having utility as fuel or as petrochemical raw materials.
Waste rubber and plastics are not conveniently burned; sulfur is released in the form of sulfur oxides which must be removed from the combustion gases prior to their discharge to the atmosphere. Rubber and plastics disposed of in incinerators melt and stick to the grate of the incinerator, causing high temperatures at the grate which can damage the incinerator.
It has been proposed to pyrolytically decompose rubber and plastic wastes by feeding the wastes either directly or in the molten state to a pyrolysis reaction furnace and maintaining the wastes therein for a sufficient period of time to decompose the wastes. For example, U.S. Pat. No. 3,956,414 describes a method of converting solid, amorphous polyolefin material to a liquid oil product which comprises melting the polyolefin by heating with a petroleum hydrocarbon oil and thermally cracking the resulting melt at a temperature of about 250.degree. to 450.degree. C. Other variations of the pyrolytic decomposition process are described in U.S. Pat. Nos. 3,674,433; 3,823,223; 3,832,151; and 3,984,288. The chief disadvantage of this approach is the amount of time required for the process to generate useful products in that heating times in excess of three hours are often required to decompose the rubber and plastics.
Defensive Publication No. T940,007 describes a process for the conversion of waste rubber to produce hydrocarbon gases, low-sulfur fuel oil, and a carbonaceous residue suitable for re-use as carbon black which comprises heating and reacting rubber in the presence of molten acidic halide Lewis salt catalysts.
U.S. Pat. No. 3,704,108 represents still another approach to the disposal of rubber tires. The process of that invention catalytically hydrogenates scrap tires in an autoclave reactor under hydrogen pressure ranging between about 500 to 2000 psig and temperatures ranging between about 600.degree. to 850.degree. F. The chief disadvantage of the process is the high operating costs caused by the necessity of employing added molecular hydrogen. Additional costs are incurred by the necessity of using an autoclave reactor to withstand the high operating pressures.